U.S. patent application number 11/025836 was filed with the patent office on 2006-06-29 for refrigerant charge status indication method and device.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Alan M. Finn, Timothy P. Galante, Sivakumar Gopalnarayanan, Pengju Kang, Dong Luo.
Application Number | 20060137370 11/025836 |
Document ID | / |
Family ID | 36609813 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060137370 |
Kind Code |
A1 |
Kang; Pengju ; et
al. |
June 29, 2006 |
Refrigerant charge status indication method and device
Abstract
A method and apparatus for determining the sufficiency of the
refrigerant charge in an air conditioning system by use of
temperature measurements. The temperature of the liquid refrigerant
leaving the condenser coil and the outdoor temperature are sensed
and representative electrical signals are generated. The electrical
signals are converted to digital values that are than compared to
predetermined optimal values to determine whether the system is
properly charged with refrigerant. An appropriate LED is lighted to
indicate that the system is undercharged, overcharged or properly
charged. For non-TXV/EXV systems a third parameter i.e. the return
air wet bulb temperature is also sensed and a representative
digital value thereof is included in the comparison with the
predetermined known values to determine if the charge is
proper.
Inventors: |
Kang; Pengju; (Hartford,
CT) ; Finn; Alan M.; (Hebron, CT) ;
Gopalnarayanan; Sivakumar; (Simsbury, CT) ; Luo;
Dong; (South Windsor, CT) ; Galante; Timothy P.;
(West Hartford, CT) |
Correspondence
Address: |
WALL MARJAMA & BILINSKI
101 SOUTH SALINA STREET
SUITE 400
SYRACUSE
NY
13202
US
|
Assignee: |
Carrier Corporation
1 Carrier Place
Farmington
CT
06434
|
Family ID: |
36609813 |
Appl. No.: |
11/025836 |
Filed: |
December 27, 2004 |
Current U.S.
Class: |
62/149 ;
62/129 |
Current CPC
Class: |
F25B 2700/21163
20130101; F25B 45/00 20130101; F25B 2700/2106 20130101; F25B
2700/04 20130101; F25B 2345/001 20130101; F25B 49/005 20130101 |
Class at
Publication: |
062/149 ;
062/129 |
International
Class: |
G01K 13/00 20060101
G01K013/00; F25B 45/00 20060101 F25B045/00 |
Claims
1. A method of determining the sufficiency of refrigerant charge in
an air conditioning system having a compressor, a condenser coil,
an expansion device and an evaporator coil connected in serial
refrigerant flow relationship, comprising the steps of: sensing the
temperature of the refrigerant leaving the condenser coil and
generating a first electrical signal representative thereof;
sensing the outdoor temperature and generating a second electrical
signal representative thereof; converting said first and second
electrical signals to first and second digital values; and
comparing first and second digital values with predetermined
optimal values to determine whether a proper refrigerant charge
condition exists.
2. A method as set forth in claim 1 wherein said outdoor
temperature is sensed by a standalone temperature sensor and said
second electrical signal is generated by a variable device which is
selectively adjustable as a function of the sensed outdoor
temperature.
3. A method as set forth in claim 1 wherein said step of comparing
said first and second digital values is accomplished by way of a
computer.
4. A method as set forth in claim 1 wherein said predetermined
optimal values are empirically determined for a particular air
conditioning system.
5. A method as set forth in claim 1 wherein said predetermined
optimal values are stored in a ROM
6. A method as set forth in claim 1 and including the further steps
of: sensing an indoor air wet bulb temperature and generating a
third electrical signal representative thereof; and converting said
third electrical signal to a third digital value and including said
third digital value with said first and second digital values to be
compared with said predetermined optimal values.
7. A method as set forth in claim 6 wherein said indoor air wet
bulb temperature is sensed by a standalone sensor and said third
electrical signal is generated by way of selective adjustment of a
variable device.
8. A method as set forth in claim 1 and including the further step
of providing a visual indication of said refrigerant charge
condition.
9. A method as set forth in claim 8 wherein said visual indication
is by way of selectively lighting one of a plurality of LEDs.
10. Apparatus for determining the sufficiency of refrigerant charge
in an air conditioning system having a compressor, condenser coil,
an expansion device and an evaporator coil interconnected in serial
refrigerant flow relationship comprising: a temperature sensor for
sensing the temperature of the liquid refrigerant leaving the
condenser; a first signal generator for generating an electrical
signal representative of said sensed liquid refrigerant
temperature; a second signal generator for generating a second
electrical signal representative of a sensed outdoor temperature;
an analog-to-digital converter for converting said first and second
electrical signals to first and second digital values,
respectively; and comparing means for comparing said first and
second digital values with predetermined optimal values to
determine whether a proper refrigerant charge condition exists.
11. Apparatus as set forth in claim 10 wherein said second signal
generator comprises a variable resistance device which is
selectively adjusted to generate an electrical signal that is
representative of a sensed outdoor temperature.
12. Apparatus as set forth in claim 10 wherein said comparing means
is a computer.
13. Apparatus as set forth in claim 10 wherein said predetermined
optimal values are empirically determined for a particular air
conditioning system.
14. Apparatus as set forth in claim 10 wherein said predetermined
optimal values are stored in a ROM.
15. Apparatus as set forth in claim 10 and including a third signal
generator for generating a third electrical signal representative
of indoor wet bulb temperature.
16. Apparatus as set forth in claim 15 wherein said third
electrical signal is converted to a third digital value by said
analog-to-digital converter.
17. Apparatus as set forth in claim 16 wherein said comparing means
includes said third digital value with said first and second
digital values to be compared with said optimal values.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to air conditioning systems
and, more particularly, to a method and apparatus for determining
proper refrigerant charge in such systems.
[0002] Maintaining proper refrigerant charge level is essential to
the safe and efficient operation of an air conditioning system.
Improper charge level, either in deficit or in excess, can cause
premature compressor failure. An over-charge in the system results
in compressor flooding, which, in turn, may be damaging to the
motor and mechanical components. Inadequate refrigerant charge can
lead to increased power consumption, thus reducing system capacity
and efficiency. Low charge also causes an increase in refrigerant
temperature entering the compressor, which may cause thermal
over-load of the compressor. Thermal over-load of the compressor
can cause degradation of the motor winding insulation, thereby
bringing about premature motor failure.
[0003] Charge adequacy has traditionally been checked using either
the "superheat method" or "subcool method". For air conditioning
systems which use a thermal expansion valve (TXV), or an electronic
expansion valve (EXV), the superheat of the refrigerant entering
the compressor is normally regulated at a fixed value, while the
amount of subcooling of the refrigerant exiting the condenser
varies. Consequently, the amount of subcooling is used as an
indicator for charge level. Manufacturers often specify a range of
subcool values for a properly charged air conditioner. For example,
a subcool temperature range between 10 and 15.degree. F. is
generally regarded as acceptable in residential cooling equipment.
For air conditioning systems that use fixed orifice expansion
devices instead of TXVs (or EXVs), the performance of the air
conditioner is much more sensitive to refrigerant charge level.
Therefore, superheat is often used as an indicator for charge in
these types of systems. A manual procedure specified by the
manufacturer is used to help the installer to determine the actual
charge based on either the superheat or subcooling measurement.
Table 1 summarizes the measurements required for assessing the
proper amount of refrigerant charge. TABLE-US-00001 TABLE 1
Measurements Required for Charge Level Determination Superheat
method Subcooling method 1 Compressor suction temperature Liquid
line temperature at the inlet to expansion device 2 Compressor
suction pressure Condenser outlet pressure 3 Outdoor condenser coil
entering air temperature 4 Indoor returning wet bulb
temperature
[0004] To facilitate the superheat method, the manufacturer
provides a table containing the superheat values corresponding to
different combinations of indoor return air wet bulb temperatures
and outdoor dry bulb temperatures for a properly charged system.
This charging procedure is an empirical technique by which the
installer determines the charge level by trial-and-error. The field
technician has to look up in a table to see if the measured
superheat falls in the correct ranges specified in the table. Often
the procedure has to be repeated several times to ensure the
superheat stays in a correct range specified in the table.
Consequently this is a tedious test procedure, and difficult to
apply to air conditioners of different makers, or even for
equipment of the same maker where different duct and piping
configurations are used. In addition, the calculation of superheat
or subcool requires the measurement of compressor suction pressure,
which requires intrusive penetration of pipes.
[0005] In the subcooling method, as with the superheat method, the
manufacturer provides a table listing the liquid line temperature
required as a function of the amount of subcooling and the liquid
line pressure. Once again, the field technician has to look up in
the table provided to see if the measured liquid line temperature
falls within the correct ranges specified in the table. Thus, this
charging procedure is also an empirical, time-consuming, and a
trial-and-error process.
SUMMARY OF THE INVENTION
[0006] Briefly, in accordance with one aspect of the invention, a
simple and inexpensive refrigerant charge inventory indication
method and apparatus using temperature measurements only is
provided for an air conditioning system.
[0007] In accordance with another aspect of the invention, the
condensing liquid line and outdoor temperatures are sensed and
representative electrical signals are generated. The signals are
converted to digital form and sent to a CPU for comparison with
stored values determined empirically in advance. On the basis of
these comparisons, an appropriate LED is activated to indicate
whether the system is properly or improperly charged with
refrigerant.
[0008] By yet another aspect of the invention, in addition to the
condensing liquid line temperature and outdoor temperature, the
return air temperature is also sensed and a representative
electrical signal generated and converted to a digital signal for
comparison with the stored values by the CPU. This additional step
is preferred for use in non-TXV/EXV systems.
[0009] By still another aspect of the invention, the sensed
temperatures may be automatically converted to representative
electrical signals, or as an alternative, the temperatures may be
sensed by stand alone instruments, with the temperatures being
dialed in by an operator to obtain representative electrical
signals.
[0010] In the drawings as hereinafter described, preferred and
alternative embodiments are depicted; however, various other
modifications and alternate constructions can be made thereto
without departing from the true spirit and scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic illustration of an air conditioning
system with present invention incorporated therein.
[0012] FIG. 2 is an electrical circuit diagram of one embodiment of
the present invention.
[0013] FIG. 3 is front view of the panel of a charge indicator in
accordance with one embodiment of the present invention.
[0014] FIG. 4 is a graphic illustration of the relationship between
charge in a system and the approach temperature (subsequently
defined) thereof.
[0015] FIG. 5 is a graphic illustration or charge map indicating
how the approach temperature varies in response to refrigerant
charge, and varying indoor and outdoor conditions.
[0016] FIG. 6 is a flow chart indicating the steps involved in the
diagnostic algorithm of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] Referring now to FIG. 1, the invention is shown generally at
10 as incorporated into an air conditioning system having a
compressor 11, a condenser 12, an expansion device 13 and an
evaporator 14. In this regard, it should be recognized that the
present invention is equally applicable for use with heat pump
systems.
[0018] In operation, the refrigerant flowing through the evaporator
14 absorbs the heat in the indoor air being passed over the
evaporator coil by the evaporator fan 16, with the cooled air than
being circulated back into the indoor air to be cooled. After
evaporation, the refrigerant vapor is pressurized in the compressor
11 and the resulting high-pressure vapor is condensed into liquid
refrigerant at the condenser 12, which rejects the heat in the
refrigerant to the outdoor air being circulated over the condenser
coil 12 by way of the condenser fan 17. The condensed refrigerant
is than expanded by way of an expansion device 13, after which the
saturated refrigerant liquid enters the evaporator 14 to continue
the cooling process.
[0019] In a heat pump, during cooling mode, the process is
identical to that as described hereinabove. In the heating mode,
the cycle is reversed with the condenser and evaporator of the
cooling mode acting as an evaporator and condenser,
respectively.
[0020] It should be mentioned that the expansion device 13 may be a
valve such as a TXV or an EXV which regulates the amount of liquid
refrigerant entering the evaporator 14 in response to the superheat
condition of the refrigerant entering the compressor 11. It may
also be a fixed orifice, such as a capillary tube or the like.
[0021] In accordance with the present invention, there are only two
measured variables needed for assessing the charge level in a
TXV/EXV based air conditioning system. These measured variables are
liquid line temperature T.sub.liquid and outdoor temperature
T.sub.outdoor which are measured by sensors S.sub.1 and S.sub.2,
respectively. These temperature sensors are thermocouples,
thermistors, or the like, and the sensed temperatures are processed
in a manner to be described hereinafter.
[0022] In a non-TXV/EXV system a third parameter is sensed i.e. the
return air wet bulb temperature, which is indicative of the
humidity. This temperature is processed along with the other two
sensed temperatures as will be more fully described
hereinafter.
[0023] Referring now to FIG. 2, there is shown circuitry that can
be used to implement the present invention. A thermistor 18 is
provided to sense the condenser liquid line temperature and convert
the sensed temperature into a voltage signal. A reference resistor
19 with known resistance value is connected in series with a DC
power supply and the thermistor 18. The voltage of the DC power
supply and the value of the reference resistor 19 are determined on
the basis of the range of temperatures of interest. The voltage
signal representative of the sensed liquid line temperature T.sub.L
is passed to A/D converter 21 with the resulting digital output
then being passed to a CPU 22 for processing in a manner to be
described hereinafter.
[0024] In addition to the voltage signal representative of the
liquid line temperature, a voltage signal is also sent to the A/D
converter 21 to represent the sensed outdoor temperature T.sub.OD.
In its simplest form, a technician or operator may measure the
outdoor temperature using a commercially available thermometer and
manually adjust the present device in order to send the
representative voltage signal to the A/D converter 21. This is
accomplished by manually adjusting the knob 23 (see FIG. 3) to the
appropriate position. The knob 23 is attached to a variable
resistor 24 that is appropriately calibrated such that when the DC
voltage is applied across the variable resistor 24 and a fixed
resistor 26, a change of knob position will produce a voltage level
that represents the particular outdoor temperature sensed.
[0025] After the electrical signals representative of the sensed
liquid line temperature T.sub.L and to the outdoor temperature
T.sub.OD have been converted to digital values by the A/D converter
21 and sent to the CPU 22, the CPU compares the representative
digital values with known stored values in a read only memory (ROM)
25 or other storage device to determine whether the system is
adequately charged with refrigerant. As a result of the comparison
the CPU 22 will send an electrical signal to the appropriate one of
the three LEDs so as to light one of the three indicators 27, 28 or
29 indicating that the system is undercharged, properly charged or
overcharged, respectively. The operator can then take whatever
action is necessary in order to bring the system into a properly
charged condition.
[0026] In non-TXV/EXV systems, a third parameter is required in
order to obtain a meaningful determination as to the adequacy of
the refrigerant charge in a system. This third parameter is the
indoor or return air wet bulb temperature T.sub.WB that can be
obtained by a technician or operator using a commercially available
humidity sensor. This value is inputted into the device by way of
the knob 31 which is selectively moved to a position so as to set
the variable resistor 32 such that, when the DC voltage is applied,
across the variable resistor 32 and a fixed resistor 33 it causes,
a specific voltage will be produced to represent the return air wet
bulb temperature T.sub.WB that has been sensed. Again, the
resulting electrical signal is sent to the A/D converter 21 and a
representative digital value is sent to the CPU 22 for processing.
Again, the resulting value is applied by the CPU 22 to send an
appropriate signal to one of the three LEDs so as to light the
appropriate indicator 27, 28 or 29.
[0027] The device as described hereinabove, which relies on an
operator using standalone sensors and then manually inputting the
resulting temperatures into the device, is a simple low cost
approach to obtain an indication of refrigerant charge adequacy in
a system. However, an alternative is for the temperature and/or
humidity sensors to be built-in as an integral part of the system
such that electrical signals representative of those temperatures
can automatically be sent directly to the A/D converter 21 and
processed as described hereinabove. In such case, the knobs 23 and
31 and their associated circuitry would not be required. This
latter approach would be difficult to implement in older systems
existing in the field since the cost would probably not be
commercially feasible.
[0028] In the implementation of the present invention in diagnosing
charge adequacy in an air conditioning system, a parameter defined
as the approach temperature (APT) is used. In a cooling system, the
condenser APT is defined as the difference in temperature between
the inlet air temperature (i.e. the outdoor air temperature
T.sub.OD) and the refrigerant temperature exiting the condenser
(T.sub.L), or APT=T.sub.L-T.sub.OD.
[0029] The APT is affected by a number of variables including
indoor air condition (i.e. dry bulb air temperature and relative
humidity) and outdoor temperature. FIG. 4 illustrates how APT
changes as a function of charge at a given indoor and outdoor
temperature. An overcharged cooling system will have lower APT than
expected, while undercharged systems will have a higher APT
value.
[0030] If a system is significantly undercharged its operation
becomes unstable and the present method and apparatus is not likely
to be successfully used. However, when a typical cooling system is
newly installed, the unit would normally be charged to a point at
or near the optimal point A as shown in FIG. 4. This point is
normally the charge amount specified by the manufacturer of a
standard configuration. With this kind of charge condition and for
conditions where the system is moderately undercharged or
overcharged, a system would normally be running in a steady state
condition and the present invention is applicable thereto.
[0031] If a map or table is available that characterizes optimal
APTs for various indoor/outdoor conditions, then such a map can be
used to charge a system to its optimal point. Such a map is shown
in FIG. 5 wherein, as an example, a 36,000 BTU per hour residential
cooling system was test run with varying charges, indoor relative
humidity and outdoor conditions. For this simulation, it was
assumed that data was required for charge diagnostics of a
non-TXV/EXV system such that the use of the APT as a charge
indicator requires the measurements of outdoor temperature and
either indoor wet bulb temperature or both indoor dry bulb and
relative humidity. In the present case, measurements were taken at
an indoor temperature at 80.degree. F. and at relative humidity
values of 0.3, 0.5, and 0.7.
[0032] It was recognized that at low outdoor temperature, the
relationship between charge and APT is well defined under different
outdoor conditions. When indoor temperatures (T.sub.id) are fixed
the indoor relative humidity (RH) affects the APT at all charge
conditions. In the real environment, indoor temperatures can, of
course, vary significantly. Since the combination of dry bulb
temperature and relative humidity is reflected in the wet bulb
measurements, the indoor wet bulb temperature, as well as the
outdoor temperature is essential in evaluating the charge in a
non-TXV/EXV system.
[0033] The data shown in FIG. 5 indicates how the APT varies in
response to charges in refrigerant charge, indoor conditions and
outdoor conditions. This set of data, which is known as a charge
map, can be obtained in the test chamber by conducting a series of
test on the unit. After the map is generated, it can than be
programmed into the ROM 25 of the diagnostic device. For this
purpose, it will be recognized that the map can be either
programmed as a table in the charge indicator or as a function.
Once the map is established in the device, it can be used for
charge diagnostics in the field.
[0034] While the present description relates to a charge map for a
particular manufacturers make and model of an air conditioning
unit, the charge map for other manufacturers units of many makes
and models can be stored in the ROM 25 with additional user input,
preferably by menu selection, to choose the appropriate charge
map.
[0035] In addition to the charge map, the ROM 25 also has a
diagnostic algorithm stored therein for purposes of automatically
stepping through the process of charge diagnostics. The diagnostic
algorithm is shown in FIG. 6 hereof.
[0036] At block 41, the outdoor temperature T.sub.OD is sensed by
an operator and manually set into the apparatus by turning the
appropriate knob 23 of the diagnostic apparatus. If the system is a
non-TXV/EXV system, the operator is also required to sense the
indoor wet bulb temperature T.sub.wb and input that data into the
device by way of the knob 31 as shown in block 42. Of course, the
charge map for the particular unit has already been stored in the
ROM as shown at block 43. With inputs from blocks 41, 42, and 43,
the optimal APT for the unit is determined at block 44.
[0037] In the meantime, as shown at block 46, the liquid line
temperature T.sub.L has been automatically measured by the device
and the APT is calculated at block 47 by subtracting the outdoor
temperature T.sub.OD from the liquid line temperature T.sub.L.
[0038] The next step, which occurs at block 48, compares the
computed APT from block 47 with the optimal APT as determined in
block 44. If the actual APT exceeds the optimal APT by over a
specified range, e.g. 2.degree., than the unit under test is deemed
undercharged and an indication will be given that refrigerant
charge needs to be added as shown in block 49. If, on the other
hand, the actual APT is less than the optimal APT by a
predetermined range, e.g. 2.degree., than the unit will be
diagnosed as overcharged and an indication will be given that
refrigerant charge needs to be removed from the system as shown in
block 51. The process than continues until the measured APT is
close to the optimal APT as indicated in block 52, in which case an
indication is then provided that a correct charge condition has
been reached as shown at block 53.
[0039] For each of the blocks 49, 51 and 53, the indication that is
given to the operator is the lighting of the appropriate LED as
described hereinabove. From those indications, the operator than
proceeds appropriately until the proper charge is obtained.
[0040] While the present invention has been particularly shown and
described with reference to a preferred embodiment as illustrated
in the drawings, it will be understood by one skilled in the art
that various changes in detail may be effected therein without
departing from the true spirit and scope of the invention as
defined by the claims. In particular, the present invention
includes the equivalence of software and hardware in digital
computing and the equivalence of digital and analog hardware in
producing a particular signal indicative of charge
* * * * *